REPORT OF THE DIRECTOR I920-2I III 



the data now available. Even the ' chief lines of elevation or folding ' 

 suggested by Dr John W. Evans, are not supported, so far as Brazil 

 is concerned, by our knowledge of the local details. Over much 

 of the Archean area are scattered infaulted remnants of old Paleozoic 

 rocks." 



It appears from Branner's survey of the basement complex of 

 Brazil that the time has not yet come to draw conclusions as to the 

 original directions of trend of the Precambrian rocks. Nevertheless 

 there exist a few data of observations that at least promise to give 

 a hint as to the possible directions. These we shall briefly cite. 



Evans (1906, p. 89) found along the Madeira in Matto Grosso, 

 near the boundary of Bolivia and far away from the Cordilleras, 

 outcrops of the Precambrian complex, that show a northwest strike 

 in their foliation or one that is parallel to the western Cordilleras. 

 He believes that he can recognize this as the predominant trend 

 far to the northwest by the direction of the ridges and the courses 

 of the rivers. Suess (v. 3, pt 2, p. 533) holds the view that this 

 strike is already controlled by the orogenic movements of the Andes 

 and he pictures the overwhelming of the western portion of the fore- 

 land " Brazilia " by the gigantic folding movement of the Andes, 

 that was dir ected eastward in the Argentine chains and the adjoining 

 country to the north. He considers the isolated Sierra de Cordoba, 

 which consists almost entirely of Precambrian rocks and whose 

 folds strike predominantly N 25 W, as also due to the extensive 

 folding of the foreland and points out this folding as a unique 

 feature. 



Under these conditions the strikes of the western portion of the 

 Brazilian mass can not be safely considered as indicating the Pre- 

 cambrian strike directions of the rocks. 



We find not much better evidence in the east. The mountain 

 ranges (Sierra do Mar, Sierra de Mantiqueira, etc.) that parallel 

 the coast and which have been so carefully investigated by Orv. 

 Derby, consist of folded Precambrian rocks striking in a northeast 

 direction. But the Silurian has been found to be folded in with the 

 Precambrian and it is therefore indeterminate to what extent the 

 folding dates back to Precambrian time. We saw before that 

 Suess compares these mountain ranges to the Appalachians. 



Likewise the east-west folds of the Precambrian in northern 

 Brazil and Guiana are by the infolded Paleozoic beds proved to 

 be of younger than Precambrian age. 



In the province of Buenos Aires, in Argentina, two rrnges, the 

 Sierra de la Ventana and Sierra Tandil, exhibit Precambrian rocks 

 together with Silurian quartzite in folds that strike northwest- 



